As the cylindrical base material on which a coating is to be formed, a piston of a compressor is given as an example. A piston of a compressor is a piston in a piston type compressor used, for example, for an air-conditioning system of automobiles. It is used for compressing coolant gas etc. in a cylinder by reciprocating motion of the piston in the cylinder. A coating having a high lubrication function is applied to such a piston.
When forming a coating layer having such a high lubrication function on the surface of a piston of a compressor or other cylindrical base material or tubular base material (hereinafter, in the present specification, these will be referred to as a “cylindrical base material” to represent the same, and the term “cylindrical base material” will be used in the meaning including not only a cylindrical base material, but also a tubular base material) using a coating layer forming apparatus, part of the lubricant coating solution supplied to the coating surface of the part is scraped off by the coating former located in the vicinity of the surface of the piston and deposited on its surface. It was confirmed that when a large amount of scraped off excess lubricant coating solution build up at the coating former, the projection of the coating film became larger when the coating former was detached (separated) from the surface of the coating layer of the piston on which the lubricant coating solution was formed.
When such a large projection of the coating film is generated, it suffers from a disadvantage that a uniform coating film cannot be formed on the surface of the piston. Depending on the size of the projection of the coating film, the lubricant coating solution will sag and foaming will occur in the lubricant coating solution at the drying and baking process performed after coating the coating solution. To prevent such foaming of the lubricant coating solution, the drying time is made longer and therefore the productivity in coating the piston is lowered.
As a method for solving such a problem, Japanese Patent Application No. 11-7552 discloses, as one example, a method for removing excess lubricant coating solution deposited on a coating former by using an apparatus explained in detail later as Comparative Example 2 with reference to FIG. 14. Namely, it is a method of mounting a plurality of coating formers 119 along the surface of a rotating body, performing the coating while successively switching the coating formers 119, and removing the excess lubricant coating solution by washing in a washing tank 130.